I would reccomend you try this program for searching for packages/installing.
Alternatilvy you could just
yay -S stacer
I don’t use appimages so cannot advise you how to do it this way. But there seems to be an older post on the forum here How to Setup an Appimage as a Startup Application? - #2 by jiibus
Were they have ended up just installing instead of using appimages instead
And just another useful bit of information for you